Institute of Image Processing and Pattern Recognition, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China.
Med Phys. 2013 Nov;40(11):111919. doi: 10.1118/1.4826173.
Small calcifications are often the earliest and the main indicator of breast cancer. Dual-energy digital mammography (DEDM) has been considered as a promising technique to improve the detectability of calcifications since it can be used to suppress the contrast between adipose and glandular tissues of the breast. X-ray scatter leads to erroneous calculations of the DEDM image. Although the pinhole-array interpolation method can estimate scattered radiations, it requires extra exposures to measure the scatter and apply the correction. The purpose of this work is to design an algorithmic method for scatter correction in DEDM without extra exposures.
In this paper, a scatter correction method for DEDM was developed based on the knowledge that scattered radiation has small spatial variation and that the majority of pixels in a mammogram are noncalcification pixels. The scatter fraction was estimated in the DEDM calculation and the measured scatter fraction was used to remove scatter from the image. The scatter correction method was implemented on a commercial full-field digital mammography system with breast tissue equivalent phantom and calcification phantom. The authors also implemented the pinhole-array interpolation scatter correction method on the system. Phantom results for both methods are presented and discussed. The authors compared the background DE calcification signals and the contrast-to-noise ratio (CNR) of calcifications in the three DE calcification images: image without scatter correction, image with scatter correction using pinhole-array interpolation method, and image with scatter correction using the authors' algorithmic method.
The authors' results show that the resultant background DE calcification signal can be reduced. The root-mean-square of background DE calcification signal of 1962 μm with scatter-uncorrected data was reduced to 194 μm after scatter correction using the authors' algorithmic method. The range of background DE calcification signals using scatter-uncorrected data was reduced by 58% with scatter-corrected data by algorithmic method. With the scatter-correction algorithm and denoising, the minimum visible calcification size can be reduced from 380 to 280 μm.
When applying the proposed algorithmic scatter correction to images, the resultant background DE calcification signals can be reduced and the CNR of calcifications can be improved. This method has similar or even better performance than pinhole-array interpolation method in scatter correction for DEDM; moreover, this method is convenient and requires no extra exposure to the patient. Although the proposed scatter correction method is effective, it is validated by a 5-cm-thick phantom with calcifications and homogeneous background. The method should be tested on structured backgrounds to more accurately gauge effectiveness.
小的钙化点通常是乳腺癌最早出现的主要标志。双能数字乳腺 X 线摄影术（DEDM）已被认为是一种提高钙化点检测能力的有前途的技术，因为它可以用于抑制乳腺中脂肪和腺体组织之间的对比度。射线散射会导致 DEDM 图像的错误计算。虽然针孔阵列插值法可以估计散射辐射，但它需要额外的曝光来测量散射并应用校正。本工作的目的是设计一种无需额外曝光即可进行 DEDM 散射校正的算法方法。
本文基于散射辐射空间变化小和乳腺 X 线片中大多数像素是非钙化像素的知识，开发了一种用于 DEDM 的散射校正方法。在 DEDM 计算中估计散射分数，并使用测量的散射分数从图像中去除散射。散射校正方法已在具有乳腺组织等效体模和钙化体模的商业全视野数字乳腺摄影系统上实现。作者还在该系统上实现了针孔阵列插值散射校正方法。提出并讨论了两种方法的体模结果。作者比较了三种 DE 钙化图像中的背景 DE 钙化信号和钙化的对比度噪声比（CNR）：无散射校正的图像、使用针孔阵列插值方法进行散射校正的图像以及使用作者算法方法进行散射校正的图像。
作者的结果表明，可以降低背景 DE 钙化信号。使用作者的算法方法进行散射校正后，未校正数据中 1962μm 的背景 DE 钙化信号的均方根值从 194μm 降低到 194μm。使用算法方法校正散射后，未校正数据的背景 DE 钙化信号范围降低了 58%。通过使用散射校正算法和去噪，可以将最小可见钙化尺寸从 380μm 减小到 280μm。
当将所提出的算法散射校正应用于图像时，可以降低背景 DE 钙化信号，并提高钙化的对比度噪声比。该方法在 DEDM 的散射校正中具有与针孔阵列插值方法相似甚至更好的性能；此外，该方法方便，无需对患者进行额外的曝光。尽管提出的散射校正方法有效，但它是在具有钙化和均匀背景的 5cm 厚体模上验证的。该方法应在结构背景上进行测试，以更准确地评估其有效性。
